NOT HER DAY: No. 4 seed Elena Dementieva looks dejected during her 5-7, 6-4, 6-3 upset loss to Melanie Oudin during yesterday's second round at the U.S. Open.Kevin P. Coughlin

TWO match points were gone, a third pending. At age 17, one tends to live in the moment and, time and again, we have seen those moments become too big, even for aspiring contenders 10 years older than Melanie Oudin.

Oudin was close and yet so far from an upset of Elena Dementieva, the fourth-ranked player in the world, the kid’s first Arthur Ashe Stadium match, and she figured it was now or never.

“This could be my last chance,” Oudin remembered thinking. “I needed to go for a big serve and it went in.

“I just couldn’t believe it.”

This is the same teenage Wimbledon conqueror of Jelena Jankovic who writes “believe” on her sneakers, who had just finished telling reporters how she plays with “no fear.”

Certainly a contradiction, but then so have been the terms “up and coming” and “American women” ever since the spectacular breakthroughs of the Williams sisters a decade ago. Thus a teenage prodigy is forgiven for her excitement.

Venus Williams, except for the occasional odd last-minute pullout from tournaments, obviously has lived up to being the “next big thing.” So did Serena, even beating her sister to their first slam title, which took the long history of next big thing to a new level. Tracy Austin, U.S. Open champion at 16, broke down physically, but Chris Evert, a Wimbledon semifinalist at 17, did a little something with her life besides marry Greg Norman.

So, no, all the up and comers don’t burn out. Even if they did, never would the torch in search of another top American. Alas, with James Blake, long-running heir to Andy Roddick’s throne, now a No. 21 seed, the vigil remains tortured.

“We need to be pushing each other,” said Oudin. “When someone excels everyone else is going to want to excel with them.

“That’s why there are so many Russian women in the top 10, because they support each other.”

One of them, Maria Sharapova, who has lived in the U.S. since age seven, sure sounds like one of us and is just an official swearing in from becom ing one of us. But if Oudin, a dead ringer for Reese Wither spoon, is about to ring in a new era, the bell tolls to great joy.

“I think it’s really cool to be called the third- best American behind the Williams sisters,” she said.

At 5-foot-6, Oudin is never going to be another Williams, ask Martina Hingis about that, but because Oudin’s goal is to be the next Justine Henin, even better. The prematurely retired Belgian is terribly missed for the elegance she provided during a generation of tedious baseline banging.

“She proved you don’t have to be 6-foot something to be No. 1,” Oudin said. “The way she moves and uses all different shots and the entire court with dropshots and angles, she figures a way to take down players that overpower her.”

Perhaps Oudin, talking about Henin in the present tense, knows something. Hope so. Even more than another good American the women’s tour could use a mighty mite.

It’s much to live up to for the 70th ranked player in the world. But the biggest moment of her career to date didn’t get too big for this little girl, a promising sign.